linux-kernel - Re: [PATCH v6 2/2] clocksource: add J-Core timer/clocksource driver

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Message-ID: <20160824200152.33be0707@arm.com>
Date:   Wed, 24 Aug 2016 20:01:52 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Rich Felker <dalias@...c.org>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-sh@...r.kernel.org>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v6 2/2] clocksource: add J-Core timer/clocksource driver

On Wed, 24 Aug 2016 13:40:01 -0400
Rich Felker <dalias@...c.org> wrote:

[...]

> > IIUC, there is a problem with the interrupt controller where
the per irq
> > line are not working correctly. Is that correct ?  
> 
> I don't think that's a correct characterization. Rather the percpu
> infrastructure just means something completely different from what you
> would expect it to mean. It has nothing to do with the hardware but
> rather with kernel-internal choice of whether to do percpu devid
> mapping inside the irq infrastructure, and the choice at the
> irq-requester side of whether to do this is required to match the
> irqchip driver's choice. I explained this better in another email
> which I could dig up if necessary, but the essence is that
> request_percpu_irq is a misnamed and unusably broken API.

Or just one that simply doesn't fit your needs, because other
architectures have different semantics than the ones you take for
granted?

> 
> > Regarding Marc Zyngier comments about the irq controller driver being
> > almost empty, I'm wondering if something in the irq controller driver
> > which shouldn't be added before submitting this timer driver with SMP
> > support (eg. irq domain ?).  
> 
> I don't think so. At most I could make the driver hard-code the percpu
> devid model for certain irqs, but that _does not reflect_ anything
> about the hardware. Rather it just reflects bad kernel internals. It

I'd appreciate it if instead of ranting about how broken the kernel is,
you'd submit a patch fixing it, since you seem to have spotted
something that we haven't in several years of using that code on a
couple of ARM-related platforms.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny.